1. Field
Apparatuses and methods consistent with the present disclosure relate to auto focusing, and more particularly, to a solid-state image sensor, an electronic device, and an auto focusing method, for auto focusing using a phase difference of a photography surface.
2. Related Art
As examples of auto focusing technologies by a typical digital camera, contrast auto focus (AF) and phase difference AF are used.
The contrast AF refers to a method for driving a focus lens to discover a peak value of contrast of an object by a digital camera and adjusts focus. When a focal point is focused in front of the object (front focusing) or is focused behind the object (back focusing), contrast is degraded. On the other hand, when a focal point is focused at the object, the contrast is a maximum. According to the contrast AF, a point (object focal point) from which contrast is increased and then reduced needs to be discovered in order to discover a point in which contrast is a maximum, a lens is moved backward and forward. Thus, an operation in which an image is blurred and then is sharpened is repeated to focus a focal point. Likewise, according to the contrast AF, since a focal point is focused by directly moving a focus lens, an image displayed on an electronic view finder becomes blurred and focusing is lengthened. However, since a lens is directly moved, a focal point is accurately focused.
The phase difference AF refers to a method for detecting a phase difference of images formed at a solid-state image sensor to adjust focusing. The phase difference AF has characteristics whereby a phase difference increases in both cases of front focusing and back focusing. According to the phase difference AF, focusing direction information as well as a phase difference value can be recognized via a detected phase difference, and thus, focusing is possible by moving a focus lens once only. That is, a movement value of a lens based on the phase difference and the focusing direction information is pre-calculated and then the focus lens is driven once with reference to the movement value to perform focusing. Accordingly, focusing may be rapidly performed without blurring of an image displayed on an electronic view finder. However, in general, it is known that focus accuracy is degraded compared with the contrast AF.
With regard to the phase difference AF, how phase difference pixels are arranged in a solid-state image sensor is an important issue. When too large of a number of phase difference pixels are arranged in the solid-state image sensor, image resolution may be degraded, and when too small of a number of phase difference pixels are arranged in the solid-state image sensor, it is difficult to detect an accurate phase difference. In addition, an electronic device with an object imaging function supports various imaging modes such as a live view mode, a still image mode, a moving image mode, etc. In this regard, locations of readout pixels for generation of images are different in the various modes and may be changed according to imaging performance in each mode according to arrangement of phase difference pixels. Thus, there is a need for technology for arranging phase difference pixels for improving the performance of a digital camera in a solid-state image sensor using phase difference AF.